Essentially, quartz crystal watches of the type with which the present invention is concerned utilize a crystal oscillator having an output frequency which is extremely stable. This frequency is divided down into suitable clock pulses for actuating a digital display on the face of the watch.
Whether the watch employs light emitting diodes or liquid crystal type displays, in each case an illuminating means is required to render the diplay visible. In the case of the light emitting diode display, the diodes normally remain de-energized since energization thereof is the greatest source of power drain and if they remain illuminated, the power cells would have to be replaced too frequently. On the other hand, the liquid crystal displays are visible at all times but they do not exhibit a great deal of contrast and a light is typically incorporated to increase the contrast of the display. Again, the light does not remain on at all times since this would be too great a power drain from the watch battery.
WIth both of the foregoing types of displays, it is accordingly necessary to provide a switch which will close the necessary terminals to effect the desired illumination of the display.
In my copending patent applications, Ser. No. 516,688 filed Oct. 21, 1974, entitled ACTUATING MECHANISMS FOR WRIST INSTRUMENTS; Ser. No. 538,743 filed Jan. 6, 1975, entitled ACCELERATION/DECELERATION ACTUATING MECHANISM FOR WRIST INSTRUMENTS; and Ser. No. 556,335 filed Mar. 7, 1975, entitled WRIST ACTUATED PRESSURE SWITCH FOR WATCHES, there are disclosed quartz crystal type watches as discussed above wherein various types of inertia switch means or pressure switch means are described for rendering the display visible.
Since the display is only illuminated at the time a user wishes to tell the time, the face of the watch is normally dark and appears blank. There is really no convenient means for a user to be advised whether the watch is properly operating unless he actuates the display. Moreover, since the watch face essentially appears blank, the watch itself is generaly inconspicuous and thus would not attract attention as might be the case with an ornate conventional type watch. Finally, there is no readily available observable means of determining how low the battery might be and thus replacement of the battery is often done simply on a fixed time basis regardless of how many times the actuating mechanism for illuminating the readout might be used.